The present invention relates to a lead frame and a production method thereof, and a semiconductor device using the lead frame and a fabrication method thereof.
Referring to FIG. 4, there is shown one related art semiconductor device using a lead frame generally designated by character xe2x80x9caxe2x80x9d. The lead frame xe2x80x9caxe2x80x9d has a number of leads xe2x80x9cbxe2x80x9d, and a die pad xe2x80x9ccxe2x80x9d on which a semiconductor element xe2x80x9cdxe2x80x9d is bonded by means of an adhesive xe2x80x9cexe2x80x9d. It should be noted that the die pad xe2x80x9ccxe2x80x9d is depressed for making the thickness of the semiconductor device as thin as possible. Respective electrodes of the semiconductor element xe2x80x9cdxe2x80x9d are connected to the corresponding leads xe2x80x9cbxe2x80x9d via bonding wires xe2x80x9cfxe2x80x9d. The semiconductor element xe2x80x9cdxe2x80x9d thus mounted is then sealed with a sealing resin xe2x80x9cgxe2x80x9d.
Referring to FIG. 5, there is shown another related art semiconductor device using a lead frame generally designated by character xe2x80x9caxe2x80x9d. In this example, to mount a plurality of semiconductor elements xe2x80x9cdxe2x80x9d, the lead frame xe2x80x9caxe2x80x9d includes a printed circuit board xe2x80x9chxe2x80x9d having an interconnection film for connecting the plurality of semiconductor elements xe2x80x9cdxe2x80x9d to each other. To be more specific, the printed circuit board xe2x80x9chxe2x80x9d is bonded on a die pad xe2x80x9ccxe2x80x9d of the lead frame xe2x80x9caxe2x80x9d by means of an adhesive xe2x80x9cexe2x80x9d, the plurality of semiconductor elements xe2x80x9cdxe2x80x9d are mounted on the printed circuit board xe2x80x9chxe2x80x9d, electrodes of the semiconductor elements xe2x80x9cdxe2x80x9d are connected to the interconnection film on the printed circuit board xe2x80x9chxe2x80x9d via bonding wires xe2x80x9cfxe2x80x9d, and the interconnection film on the printed circuit bard xe2x80x9chxe2x80x9d is connected to leads xe2x80x9cbxe2x80x9d via bonding wires xe2x80x9cfxe2x80x9d.
In the case of mounting the plurality of semiconductor elements xe2x80x9cdxe2x80x9d, it is required to provide a number of interconnections for connecting the semiconductor elements xe2x80x9cdxe2x80x9d to each other. For the semiconductor device shown in FIG. 5, such interconnections are configured as interconnection portions obtained by patterning the interconnection film on the printed circuit board xe2x80x9chxe2x80x9d.
The related art semiconductor device shown in FIG. 4, however, has a problem that it cannot incorporate a plurality of semiconductor elements xe2x80x9cdxe2x80x9d because the lead frame xe2x80x9caxe2x80x9d has no function as interconnections for connecting the plurality of semiconductor elements xe2x80x9cdxe2x80x9d to each other.
In recent years, along with strong demands toward multiple functions, higher degree of integration, and miniaturization of semiconductor devices, it has been required to incorporate a plurality of semiconductor elements (LSI chips) in one semiconductor device. From this viewpoint, the semiconductor device shown in FIG. 4, which cannot meet such a requirement, should be regarded as being poor in usability.
On the contrary, the semiconductor device shown in FIG. 5 can mount a plurality of semiconductor elements xe2x80x9cdxe2x80x9d by connecting them to each other via the printed circuit board xe2x80x9chxe2x80x9d, and therefore, it can meet the above-described demands toward multiple functions and higher degree of integration, and the like. In this regard, the semiconductor device shown in FIG. 5 is superior to the semiconductor device shown in FIG. 4.
The semiconductor device shown in FIG. 5, however, has problems caused by use of the printed circuit board xe2x80x9chxe2x80x9d. The first problem lies in that since the printed circuit board xe2x80x9chxe2x80x9d is additionally provided, the thickness of the semiconductor device is correspondingly increased. For a semiconductor device particularly required to be thinly designed, even a slight increase in thickness equivalent to the thickness of a printed circuit board may be often non-negligible.
The second problem lies in that a positional deviation inevitably occurs between the printed circuit board xe2x80x9chxe2x80x9d and the lead frame xe2x80x9caxe2x80x9d upon connection therebetween, with a result that it is difficult to ensure a necessary accuracy in positioning the printed circuit board xe2x80x9chxe2x80x9d to the lead frame xe2x80x9caxe2x80x9d.
The third problem lies in that since the production process requires the additional step of connecting the bonding wires xe2x80x9cfxe2x80x9d made from gold or the like to the interconnection film on the printed circuit board xe2x80x9chxe2x80x9d by means of expensive means such as brazing, the production cost is raised, for example. Although the technique of bonding the wires xe2x80x9cfxe2x80x9d made from gold or the like to the lead frame xe2x80x9caxe2x80x9d has been already established, the technique of connecting the wires xe2x80x9cfxe2x80x9d to the printed circuit board xe2x80x9chxe2x80x9d by means of die bonding or wire bonding has been little performed, and therefore, has been not established yet. As a result, if the technique of connecting the wires xe2x80x9cfxe2x80x9d to the printed circuit board xe2x80x9chxe2x80x9d is carried out, there occur inconveniences associated with degradation in yield, reliability, and cost. That is to say, the process of producing the semiconductor device shown in FIG. 5 by using the technique of connecting the wires xe2x80x9cfxe2x80x9d to the printed circuit board xe2x80x9chxe2x80x9d is poor in practical utility.
Additionally, it may be considered to use a TAB tape in place of the printed circuit board xe2x80x9chxe2x80x9d; however, in this case, since the TAB tape must be connected to the lead frame, there arise problems that the same positional deviation as described above occurs, and that the connection of the TAB tape to the lead frame is complicated, and since the connection is performed at a high temperature, the TAB tape may be deformed due to a residual stress caused by heat generated upon high temperature connection, with a result that it is very difficult to stably connect the TAB tape to the lead frame. Accordingly, like the process of producing the semiconductor device using the printed circuit board, the process of producing the semiconductor device using the TBA tape is poor in practical utility.
An object of the present invention is to provide a lead frame having interconnection means capable of electrically connecting a plurality of semiconductor elements mounted on the lead frame, thereby mounting the plurality of semiconductor elements on one semiconductor device, and to provide a semiconductor device using the lead frame, which device can desirably mount a plurality of semiconductor elements while thinning the thickness of the semiconductor device, and which can be produced without increasing the number of assembling steps and degrading the reliability and yield.
To achieve the above object, according to a first aspect of the present invention, there is provided a lead frame including: outer leads formed by a metal base member; first interconnection film portions formed by a metal plating layer, each of which is disposed inside the outer leads in such a manner as to be connected to an inner end of one principal plane of the corresponding one of the outer leads, and at least one second interconnection film portion formed by the metal plating layer, which is disposed inside the outer leads in such a manner as not to be connected to the outer leads; and an insulating film formed to cover planes, opposed to the outer leads, of the first and second interconnection film portions, thereby holding the first and second interconnection film portions; wherein planes, opposed to the insulating film, of the first and second interconnection film portions are taken as semiconductor element mounting planes.
With this configuration, since the lead frame has the first and second interconnection film portions, semiconductor elements mounted on the lead frame can be electrically connected to each other via the second interconnection film portion not connected to the outer leads. Since the second interconnection film portion not connected to the outer leads is held by the insulating film, it can be kept in its position although being separated from the outer leads. Accordingly, a plurality of semiconductor elements can be mounted on the lead frame. Further, since the interconnection film portions are formed, inside the outer leads formed by the metal base member, on one surface side of the outer leads, and the planes, on the outer lead side, of the interconnection film portions are taken as the semiconductor mounting planes, the thickness of the portion, on which the semiconductor elements are formed, of the semiconductor device using the lead frame does not contain the thickness of the metal base member constituting the outer leads. Accordingly, it is possible to make the semiconductor device using the lead frame thinner.
According to a second aspect of the present invention, there is provided a method of producing a lead frame, including the steps of: preparing a metal base member for forming outer leads; forming interconnection film portions made from a metal on one surface of the metal base member by selective plating; etching both surfaces of the metal base member, to form at least outer leads; forming an insulating film on the surfaces of the interconnection film portions, thereby holding the interconnection film portions by the insulating film; and selectively etching the other surface of the metal base member, to expose semiconductor element mounting planes, opposed to the insulating film, of the interconnection film portions.
With this configuration, since the interconnection film portions are formed on one surface of the metal base member for forming the outer leads by selectively plating and the insulating film for holding the interconnection film portions is formed on the surfaces of the interconnection film portions, the state of holding the interconnection film portions by the insulating film can be obtained at this step. Accordingly, the second interconnection film portion for connecting the semiconductor elements to each other can be kept as being mechanically separated from the outer leads by the insulating film.
Further, since the interconnection film portions are exposed by selectively etching the metal base member so as to remove the portion, inside the outer leads, of the metal base member, the exposed planes of the interconnection film portions can be taken as the semiconductor element mounting planes. Also, since the semiconductor element mounting planes are formed on the selectively etched side of the metal base member, the thickness of the portion, on which the semiconductor elements are mounted, of the semiconductor device using the lead frame, does not contain the thickness of the metal base member constituting the outer leads. As a result, it is possible to make the semiconductor device using the lead frame thinner.
According to a third aspect of the present invention, there is provided a semiconductor device including: a lead frame including outer leads formed by a metal base member; first interconnection film portions formed, each of which is disposed inside the outer leads in such a manner as to be connected to an inner end of one principal plane of the corresponding one of the outer leads, and at least one second interconnection film portion, which is disposed inside the outer leads in such a manner as not to be connected to the outer leads; and an insulating film formed to cover planes, opposed to the outer leads, of the first and second interconnection film portions, thereby holding the first and second interconnection film portions; wherein semiconductor elements are mounted on planes, opposed to the insulating film, of the first and second interconnection film portions of the lead frame, and sealed with a sealing resin.
With this configuration, since the semiconductor device is configured by using the lead frame according to the first aspect of the present invention, it can exhibit the same advantages as those of the lead frame according to the first aspect.
According to a fourth aspect of the present invention, there is provided a method of fabricating a semiconductor device, including the steps of: preparing a metal base member for forming outer leads; forming interconnection film portions made from a metal on one surface of the metal base member by selective plating; forming an insulating film on the surfaces of the interconnection film portions, thereby holding the interconnection film portions by the insulating film; selectively etching both surfaces of the metal base member, to form at least outer leads; selectively etching the other surface of the metal base member, to expose semiconductor element mounting planes, opposed to the insulating film, of the interconnection film portions; mounting semiconductor elements on the semiconductor element mounting planes of the interconnection film portions; and sealing the semiconductor elements thus mounted with a sealing resin.
With this configuration, since the semiconductor device is fabricated by using the lead frame produced by the production method according to the second aspect of the present invention, it can exhibit the same advantages as those of the production method according to the second aspect.